The manner in which protein, phospholipid and pigment components are assembled into functional energy transducing membranes will be investigated in a bacterial model system. Results thus far in the facultatively photoheterotrophic bacterium Rhodopseudomonas sphaeroides indicate that a fraction has been isolated that is derived from areas of the membranes enriched in newly synthesized pigment-protein complexes. Pulse labeling with (35S) met and (3H)leu should permit detection of transiently labeled polypeptide species within this fraction that undergo cotranslational modification during their insertion into the membrane. An in vitro system for the synthesis of photosynthetic membrane proteins will be established that will permit analysis of immediate translational products. This system will be coupled to membrane vesicles from photosynthetically incompetent mutant strains. The restoration of light-dependent cyclic electron flow will provide a unique functional assay for a system coupling translation and insertion of membrane proteins. Sites of chromatophore phospholipid synthesis will be unambiguously localized by direct enzymatic assay and the mechanism by which phospholipid components are asymmetrically inserted into the membrane will be investigated. The proposed studies will aid in the elucidation of mechanisms involved in organelle assembly and provide a more complete understanding of this process at the molecular level.